Override the Default Endpoint

  namespace g = ::google::cloud;
  namespace gcs = ::google::cloud::storage;
  [](std::string const& bucket_name, std::string const& object_name) {
    // NOTE: the CLOUD_STORAGE_EMULATOR_HOST environment variable overrides any
    //     value provided here.
    auto client = gcs::Client(g::Options{}.set<gcs::RestEndpointOption>(
        "https://storage.googleapis.com"));
    PerformSomeOperations(client, bucket_name, object_name);
  }